Tires are typically prepared of treads of elastomer based rubber compositions which are conventionally carbon black reinforced. Sometimes tire tread rubber compositions may also be reinforced with silica by utilizing a combination of individual silica and carbon black particles. Typically the silica is a precipitated silica.
Often coupling agents are used with precipitated silica to assist in its reinforcement of elastomers with which the silica is mixed. Utilization of silica couplers for such purpose is well known to those skilled in such art.
Historically, carbon black having domains of silica on its surface has been suggested for use as reinforcement of various diene-based elastomer compositions for tire treads. Such carbon black has been taught as being prepared, for example, by co-fuming carbon black and silica at an elevated temperature. For example, see U.S. Pat. Nos. 6,172,137, 6,160,047, 6,090,880 and 6,028,137 as well as Rubber World, Apr. 2, 2002, Page 43 et al.
However, for this invention, a tire tread rubber composition is prepared by reactive mixing of the carbon black having silica domains on its surface (with the silica domains having hydroxyl groups on their surface) and coupling agent together with at least one elastomer.
By the term “reactive mixing” it is meant that, in a non-productive mixing step, the rubber composition containing the silica and coupling agent, to the exclusion of addition of free sulfur and sulfur vulcanization accelerator(s), are mixed in an internal rubber mixer under high shear mixing conditions, in a pre-extended mixing phase to a suitable temperature followed by substantially maintaining such temperature while continue to mixing said silica-containing carbon black and silica to promote a continuing reaction between siloxy groups of said coupling agent and hydroxyl groups contained on said silica domains on the surface of said silica-containing carbon black and/or silica.
The term “non-productive” mixing step is conventionally used herein to relate to a mixing step for one or more diene-based elastomers with one or more ingredients without addition of free sulfur and sulfur vulcanization accelerator(s). Consequently, the term “productive” mixing is conventionally used herein to relate to a mixing step following said non-productive mixing step(s) in which free sulfur and one or more vulcanization accelerator(s) are mixed therewith. Such non-productive and productive mixing steps are well known to those having skill in such art.
In the description of this invention, the term “phr” where used herein, and according to conventional practice, refers to “parts of a respective material per 100 parts by weight of rubber, or elastomer”.
In the description of this invention, the terms “rubber” and “elastomer” where used herein, are to be used interchangeably, unless otherwise prescribed. The terms “rubber composition”, “compounded rubber” and “rubber compound”, if used herein, are used interchangeably to refer to “rubber which has been blended or mixed with various ingredients and materials” and such terms are well known to those having skill in the rubber mixing or rubber compounding art. The terms vulcanize and cure where used therein are used interchangeably unless otherwise indicated.